1. Field of the Invention
The present invention relates to an improvement of a shock wave treatment apparatus for destroying an object, e.g., cancer cells, stone, in a subject to be examined by a focused energy of a shock wave, or to perform a treatment.
2. Description of the Related Art
A conventional shock wave treatment apparatus comprises a shock wave transducer for forming a shock wave focusing region (to be referred to as a focusing region hereinafter) for destroying an object in a subject to be examined, and an ultrasonic transducer for acquiring tomographic image information of the subject to be examined, although not particularly shown.
A tomographic image display unit displays a sound field region image in a so-called B mode based on the image information acquired by the ultrasonic transducer.
In the shock wave treatment apparatus with the above arrangement, an object to be destroyed, such as a stone, is set to fall within the focusing region. A shock wave is generated by the shock wave transducer, so that the shock wave of a high sound pressure is focused in the focusing region. Reflection of the shock wave occurs at a boundary between the object to be destroyed and living tissues due to a difference in acoustic impedanc between the object to be destroyed and the living tissues, thus causing an internal stress in the object to be destroyed. The internal stress destroys the object to be destroyed.
As described above, the object to be destroyed must fall within the focusing region. The object to be destroyed may be set to correctly fall within the focusing region at a given moment. However, when a shock wave is to be applied in practice, the object to be destroyed may be moved due to motion or breathing of the subject to be examined, and may fall outside the focusing region.
In this case, if a shock wave is generated, the object to be destroyed as a target cannot be destroyed. Normal living tissues do not cause large reflection of a shock wave, and hence, do not cause a permanent side effect. Nevertheless, a reflection-induced permanent side effect of a shock wave should be avoided. In practice, bleeding due to damaged capillaries frequently occurs upon a shock wave treatment. If the focusing region includes a portion having a large acoustic impedance, e.g., a bone, such a portion may be damaged.
In the conventional shock wave treatment apparatus, in order to avoid idle radiation of a shock wave accompanying such a danger, a variation in position of an object to be destroyed, e.g., a stone is estimated in synchronism with cardiac beats or breathing as described in an article "Japanese Patent Disclosure No. 58-130034, CB. Forsmann, Aug. 3, 1983)", and a shock wave is radiated.
In order to confirm that the object to be destroyed falls within the focusing region, a focal point marker indicating a vertex position of the focusing region is displayed on a sound field region image.
However, the prior art is based on merely estimation, and is not a reliable method for avoiding idle radiation of a shock wave.
That is, an object to be examined may sometimes undergo unexpected motion.
It is difficult for an operator to judge an overlap degree between the focusing region and the object to be destroyed within a short period of time by only display of the focal point marker. The above-mentioned prior art documents disclose no arrangement nor idea of controlling a shock wave applicator in consideration of a moving direction in an alignment operation for causing a focal point position of a shock wave to coincide with a stone or the like.
In addition, there are no known prior art documents which disclose a mechanical technique in which the moving direction of a shock wave applicator, in particular, an ultrasonic transducer as image information acquiring means is effectively regulated with respect to the present position of a stone.